The present invention relates generally to the transmission of data in a synchronous optical network, and more particularly, to transmitting routing traffic in a synchronous optical network.
As shown in FIG. 1, there are three layers in a Synchronous Optical Network (SONET) architecture. These layers include a section, a line, and a path. A section concerns communications between two adjacent network elements, referred to as a section terminating equipment (STE) 110-1 through 110-6. Regenerators 140-1 and 140-2 and add-drop multiplexers (ADM) 150-1 and 150-2 are examples of STE.
A line concerns communications between line terminating equipment (LTE) 120-1 through 120-4, such as ADMs 150-1 and 150-2. As shown in FIG. 1, a line includes one or more sections. LTEs 120-1 through 120-4 perform line performance monitoring and automatic protection switching. Regenerators generally are not LTEs, although add-drop multiplexers typically include both an STE and an LTE.
An end-to-end connection is called a path and the equipment on either end that sends or receives a signal is called path-terminating equipment (PTE) 130. As shown in FIG. 1, a path includes one or more lines, each of which includes one or more sections.
SONET includes a section data communications channel (SDCC) providing a 192 kbps channel and a Line Data Communications Channel (LDCC) providing a 576 kbps channel.
SONET presently uses the Intermediate System to Intermediate System (IS-IS) level 2 routing protocol for exchanging routing traffic between Intermediate Systems in different areas within the same routing domain. An Intermediate System is typically defined as a router.
Presently, IS-IS level 2 traffic is sent over the SDCC. As stated above, the SDCC provides only a 192 kbps channel, which at present is heavily used. As currently defined, the SDCC does not have a priority mechanism for determining which information can be discarded when the SDCC channel is overloaded. Therefore, in the event the capacity of the SDCC channel is exceeded, the stack discards information without any intelligent discrimination. This can result in the loss of vital messages and lead to network failures.
Because the IS-IS level 2 protocol requires a contiguous backbone of IS Level 2 capable network elements, using the SDCC for IS-IS level 2 traffic, increases the costs of STE only equipment, such as regenerators. Because STE-only network elements are low end, cost sensitive devices, this can greatly increase network costs.
Thus, it is desirable to have a method and system for intermediate system level 2 transparency that overcomes the above and other disadvantages of the prior art.
Methods and systems consistent with the invention, as embodied and broadly described herein, comprise the step of assigning routing metric values for sending routing traffic in a network having line terminating equipment connected by an LDCC, such that routing traffic is sent across the LDCC.
In another embodiment, such methods and systems comprise a node that includes means for storing routing metric values for an LDCC and an SDCC, and means for placing routing traffic on the LDCC.
In another embodiment, such methods and systems comprise a network that includes means for assigning routing metric values to LDCC links, means for assigning routing metric values to SDCC links, means for computing a routing metric from the assigned routing metric values, and means for determining from the computed routing metrics whether to place routing traffic on the LDCC or SDCC, wherein the routing metric values are assigned such that the routing traffic is placed on the LDCC.